Existing fluorescent lamps have limitations in performance and lifetime that are undesirable in certain applications, such as providing back light for liquid crystal displays (LCDs). A typical mercury vapor (Hg) fluorescent lamp includes a phosphor coating on the inside surface of a glass tube. When the Hg vapor is ionized inside the tube, the lamp discharge emits radiation, including ultraviolet at a wavelength of 254 nm, that is converted to visible light by the phosphor coating.
The performance of a standard fluorescent lamp suffers from several shortcomings inherent in its basic design. In particular, the phosphor coating on the inside surface of a fluorescent tube is exposed to ion bombardment from the lamp discharge and to degrading radiation at a wavelength of 185 nm. This exposure to ions and radiation erodes the phosphors and causes undesirable color center formation. Furthermore, the unwanted radiation at 185 nm is merely wasted energy that lowers the overall efficiency of the lamp. The life of the phosphor coating can be extended by using a thicker phosphor layer. However, a thick phosphor layer reflects light much better than it transmits light. Thus, in applying the phosphor coating to the inside of a fluorescent tube, there is a trade-off between a thin coating that transmits light more efficiently versus a thick coating that provides a greater lifetime.
The less than optimum performance of conventional fluorescent lamps is particularly manifest in LCDs where high efficiency and long life are highly desirable. Furthermore, the light from existing fluorescent lamps is diffused rather inefficiently with reflectors and diffusers to attain the uniform illumination needed for LCDs. Thus, there is a need for a high efficiency, long life fluorescent lighting system that provides a uniform white light output.